The ontogeny of the multiple molecular forms of hemoglobin in the developing chick under normal and experimental conditions

A total of five molecular forms of hemoglobin appear during the development of the chick embryo. In the seven day embryo, the earliest stage studied, four of these forms are present. Hb I, preponderant in the early embryo, decreases to become a minor component at hatching; Hb II, a minor component in the early embryo, increases to become the major component at hatching; Hb III is present throughout as a minor component. Hb IV is first detectable in the nine day embryo and remains a minor component. Hb E is present as a minor component in the seven day embryo and is last found in the eleven day embryo. After hatching there is no further change in the hemoglobin pattern. In ovo oxygen deficiency and chromate retard the progressive shift from Hb I to Hb II. In vitro oxygen deficiency and chromate accelerate heme synthesis and preferentially the synthesis of Hb I. Cobalt in vivo results in a decrease in Hb I and a corresponding increase in Hb III and Hb IV. The in vivo incorporation of Fe59 indicates that the effect of cobalt is to enhance the rate of degradation of Hb I. The progressive shift from Hb I to Hb II which occurs in normal embryogenesis is discussed in terms of the control of hemoglobin synthesis at the translational level.